To date, the most detailed structural characterization of septins has been undertaken on those from opisthokonts, where heterooligomeric complexes polymerize end-to-end into filaments stabilized by alternating G- and NC-interfaces. These filaments are involved in a wide range of essential intracellular processes involving membranes, cytoskeletal components and other binding partners. Their central GTP-binding G-domain is highly conserved and similar to that seen in small monomeric or dimeric GTP